Overlapped multiplexing-based modulation and demodulation method and device

ABSTRACT

An overlapped multiplexing-based modulation and demodulation method and device are disclosed. In the modulation method, a precoding structure is used, and a transmit end first performs parity check product code-based coding on an input information sequence, generates a factor graph for a coding result and according to a coding rule, then performs overlapped multiplexing-based modulation and coding, and transmits a coded signal by using an antenna. In the demodulation method, a signal is transmitted by using a channel, and after receiving the signal by using an antenna, a receive end first performs digital signal processing, including processes such as synchronization and equalization, then performs overlapped multiplexing-based demodulation and decoding, and finally performs factor graph-based belief propagation decoding on a decoding result, to finally obtain a decoded sequence. In this application, a product code-based decoding method is used, a parity check code is used as a subcode, and a belief propagation idea of the factor graph is applied to a decoder end. Therefore, a parity check product code in a simple structure is used. In addition, in the method, the factor graph is used in a decoding process, thereby reducing operation complexity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of PCT/CN2017/091965,filed Jul. 6, 2017, published as WO 2018/068540, which claims thepriority of Chinese Application No. 201610886202.X, filed Oct. 10, 2016.The contents of the above-identified applications are incorporatedherein by reference in their entireties.

TECHNICAL FIELD

This application relates to the communications field, and in particular,to an overlapped multiplexing-based modulation and demodulation methodand device.

BACKGROUND

A modulation and demodulation technology based on overlappedmultiplexing (OvXDM: Overlapped X Division Multiplexing) includes aplurality of specific implementation solutions, for example, amodulation and demodulation technology based on overlapped time divisionmultiplexing (OvTDM: Overlapped Time Division Multiplexing), amodulation and demodulation technology based on overlapped frequencydivision multiplexing (OvFDM: Overlapped Frequency DivisionMultiplexing), a modulation and demodulation technology based onoverlapped code division multiplexing (OvCDM: Overlapped Code DivisionMultiplexing), a modulation and demodulation technology based onoverlapped space division multiplexing (OvSDM: Overlapped Space DivisionMultiplexing), and a modulation and demodulation technology based onoverlapped hybrid division multiplexing (OvHDM: Overlapped HybridDivision Multiplexing).

It should be noted that in OvXDM mentioned in this application, Xrepresents any domain, for example, time T, space S, frequency F, codeC, and hybrid H.

The following provides brief description by using OvTDM as an example.

First, time division (hereinafter referred to as TD) multiplexing (TDM:Time Division Multiplexing) is a technology in which a plurality ofsignal symbols occupying relatively narrow time durations share onerelatively wide time duration in digital communication. FIG. 1 is aschematic diagram of a conventional time division multiplexingtechnology.

In FIG. 1, time durations (referred to as timeslot widths inengineering) of multiplexed signal symbols are respectively T1, T2, T3,T4, . . . , and in engineering, the signal symbols usually occupy a sametimeslot bandwidth. ΔT is a minimum guard timeslot, and an actual guardtimeslot width should be larger. ΔT should be greater than a sum of atransition time width of a used demultiplexing gate circuit and amaximum time jitter of a system. This is a most common time divisionmultiplexing technology. This technology is used in most existingsystems such as multichannel digital broadcast systems and multichanneldigital communications systems.

A most significant feature of this technology when it is applied todigital communications is: Multiplexed signal symbols are fully isolatedfrom each other in terms of time, without mutual interference. Themultiplexed signal symbols are not limited, and symbol durations(timeslot widths) of signals may have different widths. In addition,this technology is applicable to different communications mechanisms,provided that timeslots of the multiplexed signal symbols do not overlapor cross with each other. Therefore, this technology is most widelyused. However, such multiplexing has no effect in improving spectralefficiency of a system.

Therefore, a conventional idea is that adjacent channels do not overlapin time domain, to avoid interference between the adjacent channels.However, this technology limits improvement of spectral efficiency. Anidea of a time division multiplexing technology in the prior art is thatchannels do not need to be isolated from each other and may stronglyoverlap with each other. As shown in FIG. 2, in the prior art,overlapping between channels is considered as a new coding constraintrelationship, and corresponding modulation and demodulation technologiesare proposed based on the constraint relationship. Therefore, atechnology is referred to as overlapped time division multiplexing(OvTDM: Overlapped Time Division Multiplexing). In this technology,spectral efficiency increases proportionally with a quantity K of timesof overlapping.

Referring to FIG. 3, an overlapped time division multiplexing systemincludes a transmitter A01 and a receiver A02.

The transmitter A01 includes an overlapped time divisionmultiplexing-based modulation device 101 and a transmission device 102.The overlapped time division multiplexing-based modulation device 101 isconfigured to generate a complex modulated envelope waveform carrying aninput signal sequence. The transmission device 102 is configured totransmit the complex modulated envelope waveform to the receiver A02.

The receiver A02 includes a receiving device 201 and a sequencedetection device 202. The receiving device 201 is configured to receivethe complex modulated envelope waveform transmitted by the transmissiondevice 102. The sequence detection device 202 is configured to performdata sequence detection on the received complex modulated envelopewaveform in time domain, to perform decision output.

Usually, the receiver A02 further includes a preprocessing device 203between the receiving device 201 and the sequence detection device 202,configured to assist in forming a synchronously received digital signalsequence in each frame.

In the transmitter A01, the input digital signal sequence forms, byusing the overlapped time division multiplexing-based modulation device101, transmit signals that have a plurality of symbols overlapped intime domain; and then the transmission device 102 transmits the transmitsignals to the receiver A02. The receiving device 201 of the receiverA02 receives the signals transmitted by the transmission device 102. Thesignals form, by using the preprocessing device 203, digital signalssuitable for the sequence detection device 202 to detect and receive.The sequence detection device 202 performs data sequence detection onthe received signals in time domain, to output a decision.

Referring to FIG. 4, the overlapped time division multiplexing-basedmodulation device 101 (OvTDM modulation device) includes a waveformgeneration module 301, a shift module 302, a multiplication module 303,and a superimposition module 304.

The waveform generation module 301 is configured to generate, based on adesign parameter, an initial envelope waveform whose waveform is smoothin time domain.

The shift module 302 is configured to shift the initial envelopewaveform in time domain at a preset shift interval based on a quantityof times of overlapped multiplexing, to obtain shifted envelopewaveforms at fixed intervals.

The modulation module 305 is configured to convert an input digitalsignal sequence into a signal symbol sequence represented by usingpositive and negative symbols.

The multiplication module 303 is configured to multiply the signalsymbol sequence by offset shifted envelope waveforms at fixed intervals,to obtain modulated envelope waveforms.

The superimposition module 304 is configured to superimpose themodulated envelope waveforms in time domain, to obtain a complexmodulated envelope waveform carrying the input signal sequence.

FIG. 5 is a block diagram of the preprocessing device 203 of thereceiver A02.

The preprocessing device 203 includes a synchronizer 501, a channelestimator 502, and a digital processor 503. The synchronizer 501implements symbol time synchronization of received signals in thereceiver. Next, the channel estimator 502 estimates a channel parameter.The digital processor 503 performs digital processing on receivedsignals in each frame, to form a digital signal sequence suitable forthe sequence detection device to perform sequence detection and receive.

FIG. 6 is a block diagram of the sequence detection device 202 of thereceiver A02.

The sequence detection device 202 includes an analysis unit memory 601,a comparator 602, and a plurality of retained path memories 603 andEuclidean distance memories 604 or weighted Euclidean distance memories(not shown in the figure). In a detection process, the analysis unitmemory 601 makes a complex convolutional coding model and a trellisdiagram of the overlapped time division multiplexing system, and listsand stores all states of the overlapped time division multiplexingsystem; the comparator 602 finds, based on the trellis diagram in theanalysis unit memory 601, a path with a minimum Euclidean distance or aweighted minimum Euclidean distance to a received digital signal; andthe retained path memories 603 and the Euclidean distance memories 604or the weighted Euclidean distance memories are respectively configuredto store a retained path and an Euclidean distance or a weightedEuclidean distance that are output by the comparator 602. One retainedpath memory 603 and one Euclidean distance memory 604 or weightedEuclidean distance memory need to be prepared for each stable state.Preferably, a length of the retained path memory 603 may be 4K-5K.Preferably, the Euclidean distance memory 604 or the weighted Euclideandistance memory stores only a relative distance.

In an OvXDM system, a signal transmitter modulates a signal and thensends a modulated signal to a signal receiver, and the signal receiverdemodulates the modulated signal after receiving it. A demodulationprocess includes a decoding step (that is, the sequence detection stepperformed by the foregoing sequence detection device). In a conventionalcommunications system, a Chase algorithm is used for decoding in mostcases. The algorithm involves massive sorting operations, and acomputation amount is very large.

SUMMARY

This application provides an overlapped multiplexing-based modulationand demodulation method and device, so as to resolve a problem inconventional decoding that a Chase algorithm is used for decoding inmost cases, a process of the algorithm involves massive sortingoperations, and therefore computation complexity is relatively high.

According to a first aspect of this application, this applicationprovides an overlapped multiplexing-based modulation method, including:

obtaining input information;

performing parity check product code-based coding on the inputinformation, to generate a factor graph;

performing overlapped multiplexing-based modulation and coding; and

transmitting a coded signal.

According to a second aspect of this application, this applicationfurther provides an overlapped multiplexing-based demodulation method,including:

obtaining an input signal;

performing overlapped multiplexing-based demodulation and decoding onthe input signal;

performing factor graph-based belief propagation decoding; and

outputting a decoding result.

According to a third aspect of this application, this applicationfurther provides an overlapped multiplexing-based modulation device,including:

an input information obtaining module, configured to obtain inputinformation;

a parity check product code-based coding module, configured to performparity check product code-based coding on the input information;

an overlapped multiplexing-based modulation and coding module,configured to perform overlapped multiplexing-based modulation andcoding; and

a signal transmission module, configured to transmit a coded signal.

In an embodiment, the parity check product code-based coding moduleincludes: an information bit filling unit, configured to fill the inputinformation into information bits in a coding structure, wherespecifically, the information bit filling unit is configured to write aninput information sequent into corresponding information bits accordingto a k_(c)×k_(r) two-dimensional structure, where a length of the inputinformation is N=k_(c)×k_(r), where k_(r) represents a quantity of rows,and k_(c) represents a quantity of columns;

a row coding unit, configured to perform row coding on the informationin the information bits, where specifically, the row coding unit isconfigured to perform row coding by assuming that information in the(k_(r)+1)^(th) bit of each row is a modulo-2 addition result of thefirst k_(c) ^(th) columns of the current row;

a column coding unit, configured to perform column coding on theinformation in the information bits, where specifically, the columncoding unit is configured to perform column coding by assuming thatinformation in the (k_(c)+1)^(th) bit of each column is a modulo-2addition result of the first k_(r) ^(th) rows of the current column; and

a factor graph generation unit, configured to generate a factor graphfor a coding result according to a coding rule.

In an embodiment, the coding structure is a diagonal coding structure, atwo-dimensional coding structure, a three-dimensional coding structure,or a four-dimensional coding structure.

According to a fourth aspect of this application, this applicationfurther provides an overlapped multiplexing-based demodulation device,including:

an input signal obtaining module, configured to obtain an input signal;

an overlapped multiplexing-based demodulation and decoding module,configured to perform overlapped multiplexing-based demodulation anddecoding on the input signal;

a factor graph-based belief propagation decoding module, configured toperform factor graph-based belief propagation decoding; and

a decoding result output module, configured to output a decoding result.

In an embodiment, the factor graph-based belief propagation decodingmodule includes:

an initial log-likelihood ratio calculation unit, configured tocalculate an initial log-likelihood ratio;

a maximum-quantity-of-iterations setting unit, configured to set amaximum quantity of iterations;

a check information update unit, configured to calculate a check nodeand update check information;

an information message update unit, configured to calculate a variablenode and update an information message;

a log-likelihood ratio update unit, configured to calculate alog-likelihood ratio when all check nodes related to information bitsprovide information;

a decision unit, configured to perform decision on an informationsequence; and

a decoding result output unit, configured to output the decoding resultafter a specific preset condition is satisfied.

In an embodiment, the check information update unit is configured tocalculate the check node by using a formula

${\delta_{ij} = {{2{\tanh^{- 1}( {\prod\limits_{j^{\prime} \in {{N{(i)}}\backslash j}}\;{\tanh( {\lambda_{j^{\prime}i}/2} )}} )}\mspace{14mu}{or}\mspace{14mu}\delta_{ij}} = {{\min( {\lambda_{j^{\prime}i}} )}( {\prod\limits_{j^{\prime} \in {{N{(i)}}\backslash j}}{{sign}( \lambda_{j^{\prime}i} )}} )}}},$and update the check information, where δ_(ij) is the check information,and represents a log-likelihood ratio when other variable nodes exceptthe j^(th) variable node provide information; λ_(j′i) is the informationmessage, and represents a log-likelihood ratio when other check nodesexcept the i^(th) check node provide information; N(i) is a partialelement information set constrained by the check node; N(i)/j representsa subset of N(i) that does not include the j^(th) variable node; and Πis a continuous multiplication operation; and/or

the preset condition is that the maximum quantity of iterations isreached.

In an embodiment, the information message update unit is configured to:calculate the variable node by using a formula

${\lambda_{ji} = {{{llr}( x_{j} )} + {\sum\limits_{i^{\prime} \in {{M{(j)}}\backslash i}}\delta_{i^{\prime}j}}}},$and update the information message; and

calculate the log-likelihood ratio when all the check nodes related tothe information bits provide information by using a formula

${\lambda_{j} = {{{llr}( x_{j} )} + {\sum\limits_{i^{\prime} \in {M{(j)}}}\delta_{i^{\prime}j}}}},$where

x_(j) is a transmit codeword in a transmit signal of a transmitter;y_(j) is a receive codeword in the input signal received by a receiver;M(j) is a check set in which the variable node participates; M(j)\irepresents a subset of the M(j) that does not include the i^(th) checknode; δi′j is the check information, and represents a log-likelihoodratio when other variable nodes except the j^(th) variable node provideinformation; llr(x_(j)) is a representation form of a log-likelihoodratio when the receiver initially receives channel information; λ_(ji)is the information message, and represents a log-likelihood ratio whenother check nodes except the i^(th) check node provide information; andλ_(j) represents the log-likelihood ratio when all the check nodesrelated to the information bits provide information.

This application provides the overlapped multiplexing-based modulationand demodulation method and device. In the modulation method, aprecoding structure is used, and a transmit end first performs paritycheck product code-based coding on an input information sequence,generates a factor graph for a coding result and according to a codingrule, then performs overlapped multiplexing-based modulation and coding,and transmits a coded signal by using an antenna. In the demodulationmethod, a signal is transmitted by using a channel, and after receivingthe signal by using an antenna, a receive end first performs digitalsignal processing, including processes such as synchronization andequalization, then performs overlapped multiplexing-based demodulationand decoding, and finally performs factor graph-based belief propagationdecoding on a decoding result, to finally obtain a decoded sequence. Inthis application, a product code-based decoding method is used, a paritycheck code is used as a subcode, and a belief propagation idea of thefactor graph is applied to a decoder end. Therefore, a parity checkproduct code in a simple structure is used. In addition, in the method,the factor graph is used in a decoding process, thereby reducingoperation complexity.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a conventional time divisionmultiplexing technology;

FIG. 2 is a schematic diagram of an overlapped time divisionmultiplexing principle;

FIG. 3 is a schematic structural diagram of an overlapped time divisionmultiplexing system;

FIG. 4 is a schematic structural diagram of an overlapped time divisionmultiplexing-based modulation device;

FIG. 5 is a schematic structural diagram of a preprocessing device of areceiver;

FIG. 6 is a schematic structural diagram of a sequence detection deviceof a receiver;

FIG. 7 is a structural diagram of a parity check product code accordingto an embodiment of this application;

FIG. 8 is a two-way transfer factor graph according to an embodiment ofthis application;

FIG. 9 is a schematic diagram of a correspondence between a parity checkproduct code matrix and a factor graph according to an embodiment ofthis application;

FIG. 10 is a block diagram of a transmit end in a precoding OvXDM systemaccording to an embodiment of this application;

FIG. 11 is a schematic flowchart of an overlapped multiplexing-basedmodulation method according to an embodiment of this application;

FIG. 12 is a schematic flowchart of a parity check product code-basedcoding step in an overlapped multiplexing-based modulation methodaccording to an embodiment of this application;

FIG. 13 is a schematic flowchart of a overlapped multiplexing-basedmodulation and coding step in an overlapped multiplexing-basedmodulation method according to an embodiment of this application;

FIG. 14 is a schematic principle diagram of multiplexing of K waveforms;

FIG. 15 is a schematic principle diagram of a symbol superimpositionprocess of K waveforms;

FIG. 16 is a schematic flowchart of an overlapped multiplexing-baseddemodulation method according to an embodiment of this application;

FIG. 17 is a schematic flowchart of a decoding step in an overlappedmultiplexing-based demodulation method according to an embodiment ofthis application;

FIG. 18 is an input-output relationship tree diagram of an overlappedtime division multiplexing system when K=3;

FIG. 19 is a node state transition diagram;

FIG. 20 is a trellis diagram of an OvTDM system when K=3;

FIG. 21 is a schematic flowchart of a factor graph-based beliefpropagation decoding step in an overlapped multiplexing-baseddemodulation method according to an embodiment of this application;

FIG. 22 is a schematic diagram of modules in an overlappedmultiplexing-based modulation device according to an embodiment of thisapplication;

FIG. 23 is a schematic diagram of units of a parity check productcode-based coding module in an overlapped multiplexing-based modulationdevice according to an embodiment of this application;

FIG. 24 is a schematic diagram of modules in an overlappedmultiplexing-based demodulation device according to an embodiment ofthis application; and

FIG. 25 is a schematic diagram of units of a factor graph-based beliefpropagation decoding module in an overlapped multiplexing-baseddemodulation device according to an embodiment of this application.

DESCRIPTION OF EMBODIMENTS

First, it should be noted that, in an overlapped multiplexing(OvXDM)-based modulation and demodulation method and device provided inthis application, X represents any domain, for example, time T, space S,frequency F, code C, and hybrid H. For ease of description, embodimentsof this application are mainly described by using overlapped timedivision multiplexing (OvTDM) and overlapped frequency divisionmultiplexing (OvFDM) as examples. Persons skilled in the art should knowthat the modulation and demodulation method and device protected by theclaims of this application may also be applied to overlappedmultiplexing technologies in other domains.

In an OvXDM system, a signal transmitter modulates a signal and thensends a modulated signal to a signal receiver, and the signal receiverdemodulates the modulated signal after receiving it. A demodulationprocess includes a decoding step. During research on overlappedmultiplexing-based modulation and demodulation technologies, personsskilled in the art use conventional decoding methods. In theconventional decoding methods, a Chase algorithm is used in most cases.The algorithm involves massive sorting operations, and a computationamount is very large.

Although the existing decoding methods have the foregoing problem,because these methods have been widely used, persons skilled in the arthave fully accepted the methods, without taking efforts to look for abetter method.

In an OvXDM (X represents time T, frequency F, space S, code C, hybridH, or the like) system, an entire process usually ends after a receiveend completes waveform decoding. In a relatively complex case, the OvXDMsystem is used together with a common conventional communicationstechnology, for example, a concatenated OvXDM system or a precodingOvXDM system, to improve overall system performance. However, an errorcorrection code has a relatively good error correction capability, andcan improve overall system performance and reduce a bit error rate.Therefore, the error correction code is applied to the OvXDM system inmost cases.

A product code is an error correction code in a block structure. In theproduct code, an idea of an iteration is introduced to a decoder end, toconstruct a currently popular Turbo product code. This is TPC-basedcoding. This type of coding is very widely used in existingcommunications systems. In a conventional communications system, a Chasealgorithm is used for decoding in most cases. The algorithm involvesmassive sorting operations, and a computation amount is very large.

In the product code proposed in this application, a very simple paritycheck code is used as a subcode, and code length control and adaptationcan be performed very flexibly and conveniently. At the decoder end, aniterative decoding method based on a belief propagation idea of a factorgraph is used, and an operation is flexible and simple. In thisapplication, the decoding idea based on belief propagation of a factorgraph is introduced into a decoding method based on a parity checkproduct code.

Commonly used error correction codes include a product code (TurboProduct Code, TPC) and a low density parity check code (Low DensityParity Check Code, LDPC). In this application, a parity check productcode is used as an example. A coding structure of the parity checkproduct code is shown in FIG. 7. The coding structure is very simple,and a same code length may be selected for row and column subcodes.

According this coding structure, a factor graph is obtained in codingrelatively easily, as shown in FIG. 8. Nodes shown in a lower part ofthe figure are variable nodes, and a quantity is a code length in acoding matrix block. Nodes shown in an upper part of the figure arecheck nodes, and a quantity is a length of a check bit. When the codingstructure is applied to the OvXDM system, a relationship between acorresponding coding matrix and a two-way factor graph is shown in FIG.9. In a related factor graph constructed in the parity check productcode, it can be found that the factor graph has a relatively largegirth, is relatively applicable to decoding by using a beliefpropagation method. During belief propagation decoding, a message may bepropagated by using an operation in log domain.

The following further describes this application in detail withreference to specific embodiments and accompanying drawings.

Embodiment 1

In this embodiment, it is assumed that an input information sequence isx, an information length is N=k_(c)×k_(r)=100, k_(c)=10, k_(r)=10, and aquantity of times of overlapping is K=5, and an example is used, inwhich a multiplexing waveform is a Chebyshev window, a modulation schemeis BPSK, and a TPC error correction code is used for precoding. Using aprecoding structure shown in FIG. 10, a system processing process is: Atransmit end first performs TPC-based coding on an input informationsequence, then performs OvXDM-based coding, and transmits a coded signalby using an antenna. The signal is transmitted in a channel Afterreceiving the signal by using an antenna, a receive end first performsdigital signal processing, including processes such as synchronizationand equalization; then performs OvXDM-based decoding; and finallyperforms TPC-based decoding on a decoding result, that is, by using afactor graph-based belief propagation decoding method in thisapplication, to finally obtain a decoded sequence x′.

Commonly used OvXDM (X represents time T, frequency F, space S, code C,hybrid H, or the like)-based decoding includes a maximum likelihoodsequence decoding algorithm such as Viterbi decoding, and a maximumposterior probability algorithm such as a BCJR algorithm, a MAPalgorithm, or a Log_MAP algorithm. The following mainly describes aparity check product code-based coding process and a correspondingfactor graph-based belief propagation decoding method.

First, variables used in this embodiment are defined. It is assumed thatx_(j) is a transmit codeword, and y_(j) is a receive codeword.

N(i): a partial element information set constrained by a check node,where N(i)\j represents a subset of N(i) that does not include thej^(th) variable node.

M(j): a check set in which a variable node participates, where M(j)\irepresents a subset of M(j) that does not include the i^(th) check node.

llr(x_(j)): a representation form of a log-likelihood ratio when channelinformation is initially received.

λ_(ji): an information message, representing a log-likelihood ratio whenother check nodes except the i^(th) check node provide information.

λ_(j): an information message, representing a log-likelihood ratio whenall check nodes related to information bits provide information.

δ_(ij): check information, representing a log-likelihood ratio whenother variable nodes except the j^(th) variable node provideinformation.

Referring to FIG. 11, this embodiment provides an overlappedmultiplexing-based modulation method, including the following steps:

Step 1.1: Obtain input information. The input information is the inputdigital signal sequence in FIG. 4.

Step 1.2: Perform parity check product code-based coding on the inputinformation.

Step 1.3: Perform overlapped multiplexing-based modulation and coding.

Step 1.4: Transmit a coded signal, that is, transmit, to a receive end,a complex modulated envelope waveform generated in FIG. 4 as a transmitsignal.

Referring to FIG. 12, step 1.2 includes the following substeps:

Substep 1-1: Fill the input information into information bits in acoding structure. The coding structure may be a diagonal codingstructure, a two-dimensional coding structure, a three-dimensionalcoding structure, or four-dimensional coding structure, or ahigher-dimensional coding structure. This embodiment is described byusing the two-dimensional coding structure as an example.

Specifically, an input information sequence is written intocorresponding information bits according to a two-dimensionalk_(c)×k_(r) structure, where k_(r) represents a quantity of rows, andk_(c) represents a quantity of columns.

Substep 1-2: Perform row coding on the information in the informationbits.

Specifically, row coding is performed by assuming that information inthe (k_(r)+1)^(th) bit of each row is a modulo-2 addition result of thefirst k_(c) ^(th) columns of the current row.

Substep 1-3: Perform column coding on the information in the informationbits.

Specifically, column coding is performed by assuming that information inthe (k_(c)+1)^(th) bit of each column is a modulo-2 addition result ofthe first k_(r) ^(th) rows of the current column.

A size of matrix obtained after coding is (k_(c)+1)×(k_(r)+1). A TPCcode rate thereof is

${{Rate} = \frac{k_{c} \times k_{r}}{( {k_{c} + 1} ) \times ( {k_{r} + 1} )}},$and is 0.8264 in this embodiment.

Substep 1-4: Generate a factor graph for a coding result according to acoding rule.

As shown in FIG. 13, step 1.3 includes the following substeps:

Substep 2.1: Generate an initial envelope waveform h(t) in time domainbased on a design parameter.

During generation of the initial envelope waveform, a user may enter thedesign parameter, to implement flexible configuration in an actualsystem based on a system performance indicator.

In some embodiments, when side lobe attenuation of the initial envelopewaveform has been determined, the design parameter includes a windowlength L of the initial envelope waveform, for example, when the initialenvelope waveform is a Bartlett envelope waveform.

In some embodiments, the design parameter includes a window length L andside lobe attenuation r of the initial envelope waveform, for example,when the initial envelope waveform is a Chebyshev envelope waveform.

Certainly, when the initial envelope waveform is in another form, thedesign parameter may be determined based on characteristics of thecorresponding initial envelope waveform.

Substep 2.2: Shift the initial envelope waveform in a correspondingdomain (time domain in this embodiment) based on a quantity K of timesof overlapped multiplexing and a preset shift interval, to obtainshifted envelope waveforms h(t−i*ΔT) at fixed intervals.

The shift interval is a time interval ΔT, and the time interval ΔT is:ΔT=L/K. In this case, a symbol width of a signal is ΔT.

In addition, it further needs to be ensured that ΔT is not less than areciprocal of a system sampling rate.

A value of i is related to an input symbol length N, and i is an integerfrom 0 to N−1. For example, when N=8, i is an integer from 0 to 7.

Substep 2.3: Convert a digital signal sequence obtained after coding instep 1.2 into a signal symbol sequence represented by using positive andnegative symbols.

Specifically, 0 and 1 in the digital signal sequence are converted into+A and −A respectively, to obtain the positive-negative symbol sequence,where a value of A is any non-zero number. For example, when A is 1, aninput {0, 1} bit sequence is converted into a {+1, −1} symbol sequencethrough BPSK (binary phase shift keying) modulation.

Substep 2.4: Multiply the signal symbol sequence x_(i) (in thisembodiment, x_(i)={+1 +1 −1 −1 −1 +1 −1 +1}) obtained after conversionby the shifted envelope waveforms h(t−i*ΔT) at fixed intervals, toobtain modulated envelope waveforms x_(i) h(t−i*ΔT).

Substep 2.5: Superimpose the modulated envelope waveforms x_(i)h(t−i*ΔT) in the corresponding domain (time domain in this embodiment),to obtain a complex modulated envelope waveform carrying the inputsignal sequence, namely, a transmitted signal.

The transmitted signal may be represented as

${s(t)} = {\sum\limits_{i}{x_{i}{{h( {t - {i \times \Delta\; T}} )}.}}}$

The transmitting a coded signal in step 1.4 means: transmitting theobtained complex modulated envelope waveform as the transmit signal.

Therefore, in this embodiment, when the value of A is 1, output signals(the output signal symbol sequence) obtained after superimposition are:s(t)={+1 +2 +1 −1 −3 −1 −1 +1}.

Referring to FIG. 14, FIG. 14 is a schematic principle diagram ofmultiplexing of K waveforms. The diagram is in a shape of aparallelogram. Each row represents a to-be-sent signal waveformx_(i)h(t−i*ΔT) obtained after a to-be-sent symbol x_(i) is multiplied byan envelope waveform h(t−i*ΔT) of a corresponding moment. a₀ to a_(k-1)represent a coefficient value of each part obtained after each windowfunction waveform (an envelope waveform) is segmented for K times, andare specifically a coefficient related to an amplitude.

When the input digital signal sequence is converted into thepositive-negative symbol sequence, 0 and 1 in the input digital signalsequence are converted into ±A, to obtain the positive-negative symbolsequence, where the value of A is any non-zero number. For example, whenthe value of A is 1, the input {0, 1} bit sequence is converted into the{+1, −1} symbol sequence through BPSK modulation, to obtain thepositive-negative symbol sequence. Therefore, FIG. 15 is a schematicprinciple diagram of a symbol superimposition process of K waveforms. Inthe superimposition process in FIG. 15, left three numbers in the firstrow represent the first input symbol +1, left three numbers in thesecond row represent the second input symbol +1, left three numbers inthe third row represent the third input symbol −1, middle three numbersin the first row represent the fourth input symbol −1, middle threenumbers in the second row represent the fifth input symbol −1, middlethree numbers in the third row represent the sixth input symbol +1,right three numbers in the first row represent the seventh input symbol−1, and right three numbers in the second row represent the eighth inputsymbol +1. Therefore, after three waveforms are superimposed, obtainedoutput symbols are {+1 +2 +1 −1 −3 −1 −1 +1}.

Certainly, if the input symbol length is another value, superimpositionmay be performed based on the manner shown in FIG. 14 and FIG. 15, toobtain output symbols.

It should be noted that, in step 1.3, overlapped multiplexing-basedmodulation and coding may also be performed by using any feasible methodin the prior art, in addition to the foregoing method.

Embodiment 2

Based on the overlapped multiplexing-based modulation method provided inEmbodiment 1, this embodiment correspondingly provides an overlappedmultiplexing-based demodulation method. Referring to FIG. 16, theoverlapped multiplexing-based demodulation method includes the followingsteps:

Step 3.1: Obtain an input signal. The input signal is the complexmodulated envelope waveform signal transmitted in FIG. 4.

Step 3.2: Perform overlapped multiplexing-based demodulation anddecoding on the input signal.

Step 3.3: Perform factor graph-based belief propagation decoding.

Step 3.4: Output a decoding result.

Referring to FIG. 17, in this embodiment, step 3.2 specifically includesthe following sub steps:

(1) First, synchronize received signals, including carriersynchronization, frame synchronization, symbol time synchronization, andthe like.

(2) Perform digital processing on received signals in each frame basedon a sampling theorem.

(3) Cut a received waveform based on a waveform transmission timeinterval.

(4) Decode the waveform obtained after cutting based on a decodingalgorithm. For a decoding process, referring to FIG. 18, FIG. 18 is aninput-output relationship diagram of overlapped time division when K=3.FIG. 19 is a node state transition diagram. FIG. 20 is a trellis diagramof an OvTDM system when K=3. Viterbi (Viterbi) decoding is a most widelyused method in a convolutional code. A basic idea of the Viterbidecoding is: traversing all paths in the trellis diagram, comparingdistances between a plurality of branches arriving at each state and acorrect path in a state transition process in the trellis diagram,retaining only a path with a smallest distance, and obtaining anestimate of the correct path through comparison and screening, toimplement decoding.

It should be noted that the overlapped multiplexing-based demodulationand decoding in step 3.2 may be performed by using the foregoing method,or may be performed in another feasible method in the prior art.

Referring to FIG. 21, assuming that a noise variance obtained afterdigital signal processing is σ, and a sequence obtained afterOvXDM-based decoding is x_(j)∈{+1, −1}, step 3.3. includes the followingsubsteps:

Substep 3-1: Calculate an initial log-likelihood ratio.

Specifically, a result of a log-likelihood ratio is usually related to amodulation scheme, a decoding method of the OvXDM system (namely, theoverlapped multiplexing-based demodulation and decoding method), and thelike, with an ultimate objective to extract a soft value.

Substep 3-2: Set a maximum quantity of iterations.

Specifically, in this embodiment, a quantity of iterations is set to 50.When the quantity of iterations increases, a final decoded sequence iscloser to an theoretical sequence. However, if the quantity ofiterations is excessively large, algorithm complexity alsocorrespondingly increases.

Substep 3-3: Calculate a check node and update check information.

Specifically, check nodes of each row and each column are calculated andupdated based on a formula

${\delta_{ij} = {2{\tanh^{- 1}( {\prod\limits_{j^{\prime} \in {{N{(i)}}\backslash j}}\;{\tanh( {\lambda_{j^{\prime}i}\text{/}2} )}} )}}},$where Π is a continuous operation.

Substep 3-4: Calculate a variable node and update an informationmessage.

Specifically, information messages of each row and each column areupdated based on a formula

$\lambda_{ji} = {{{llr}( x_{j} )} + {\sum\limits_{i^{\prime} \in {{M{(j)}}\backslash i}}{\delta_{i^{\prime}j}.}}}$

Substep 3-5: Calculate a log-likelihood ratio when all check nodesrelated to information bits provide information.

Specifically, a new information message is calculated based on a formula

$\lambda_{j} = {{{llr}( x_{j} )} + {\sum\limits_{i^{\prime} \in {M{(j)}}}{\delta_{i^{\prime}j}.}}}$

Substep 3-6: Perform decision.

Specifically, in this embodiment, a hard decision manner and a BPSKmodulation scheme are used. It is assumed that corresponding modulationmapping herein is 1→−1, 0→+1, that is,

${\hat{x}}_{j} = \{ {\begin{matrix}{0,} & {\lambda_{j} \geq 0} \\{1,} & {\lambda_{j} < 0}\end{matrix}.} $

Substep 3-7: Output the decoding result after a specific presetcondition is satisfied. In this embodiment, the preset condition is thatthe maximum quantity of iterations is reached.

It is determined whether the maximum quantity of iterations is reached.If the condition is satisfied, current decoding ends, and the decodedsequence is output; otherwise, calculation is performed again, startingfrom substep 3-3. In this case, the information message λ_(ji) is aresult of a previous iteration operation.

Embodiment 3

Referring to FIG. 22, based on the overlapped multiplexing-basedmodulation method provided in Embodiment 1, this embodimentcorrespondingly provides an overlapped multiplexing-based modulationdevice, including an input information obtaining module A11, a paritycheck product code-based coding module A12, an overlappedmultiplexing-based modulation and coding module A13, and a signaltransmission module A14.

The input information obtaining module A11 is configured to obtain inputinformation.

The parity check product code-based coding module A12 is configured toperform parity check product code-based coding on the input information.

The overlapped multiplexing-based modulation and coding module A13 isconfigured to perform overlapped multiplexing-based modulation andcoding.

The signal transmission module A14 is configured to transmit a codedsignal.

Referring to FIG. 23, in this embodiment, the parity check productcode-based coding module A12 includes an information bit filling unitA21, a row coding unit A22, a column coding unit A23, and a factor graphgeneration unit A24.

The information bit filling unit A21 is configured to fill the inputinformation into information bits in a coding structure. The codingstructure may be a diagonal coding structure, a two-dimensional codingstructure, a three-dimensional coding structure, or four-dimensionalcoding structure, or a higher-dimensional coding structure. Thisembodiment is described by using the two-dimensional coding structure asan example.

Specifically, the information bit filling unit is configured to write aninput information sequent into corresponding information bits accordingto a k_(c)×k_(r) two-dimensional structure, where a length of the inputinformation is N=k_(c)×k_(r), where k_(r) represents a quantity of rows,and k_(c) represents a quantity of columns.

The row coding unit A22 is configured to perform row coding on theinformation in the information bits. Specifically, the row coding unitis configured to perform row coding by assuming that information in the(k_(r)+1)^(th) bit of each row is a modulo-2 addition result of thefirst k_(c) ^(th) columns of the current row.

The column coding unit A23 is configured to perform column coding on theinformation in the information bits. Specifically, the column codingunit is configured to perform column coding by assuming that informationin the (k_(c)+1)^(th) bit of each column is a modulo-2 addition resultof the first k_(r) ^(th) rows of the current column.

The factor graph generation unit A24 is configured to generate a factorgraph for a coding result according to a coding rule.

The overlapped multiplexing-based modulation device provided in thisembodiment is corresponding to the overlapped multiplexing-basedmodulation method provided in Embodiment 1. Therefore, a principle ofthe device is not described in detail herein.

Embodiment 4

Referring to FIG. 24, based on the overlapped multiplexing-baseddemodulation method provided in Embodiment 2, this embodimentcorrespondingly provides an overlapped multiplexing-based demodulationdevice, including an input signal obtaining module B11, an overlappedmultiplexing-based demodulation and decoding module B12, a factorgraph-based belief propagation decoding module B13, and a decodingresult output module B14.

The input signal obtaining module B11 is configured to obtain an inputsignal.

The overlapped multiplexing-based demodulation and decoding module B12is configured to perform overlapped multiplexing-based demodulation anddecoding on the input signal.

The factor graph-based belief propagation decoding module B13 isconfigured to perform factor graph-based belief propagation decoding.

The decoding result output module B14 is configured to output a decodingresult.

Referring to FIG. 25, in this embodiment, the factor graph-based beliefpropagation decoding module B13 includes an initial log-likelihood ratiocalculation unit B21, a maximum-quantity-of-iterations setting unit B22,a check information update unit B23, an information message update unitB24, a log-likelihood ratio update unit B25, a decision unit B26, and adecoding result output unit B27.

The initial log-likelihood ratio calculation unit B21 is configured tocalculate an initial log-likelihood ratio.

The maximum-quantity-of-iterations setting unit B22 is configured to seta maximum quantity of iterations.

The check information update unit B23 is configured to calculate a checknode and update check information.

The information message update unit B24 is configured to calculate avariable node and update an information message.

The log-likelihood ratio update unit B25 is configured to calculate alog-likelihood ratio when all check nodes related to information bitsprovide information.

The decision unit B26 is configured to perform decision.

The decoding result output unit B27 is configured to output the decodingresult after a specific preset condition is satisfied. The presetcondition may be that the maximum quantity of iterations is reached.

Specifically, in this embodiment, a hard decision manner and a BPSKmodulation scheme are used. It is assumed that corresponding modulationmapping herein is 1→−1, 0→+1, that is,

${\hat{x}}_{j} = \{ {\begin{matrix}{0,} & {\lambda_{j} \geq 0} \\{1,} & {\lambda_{j} < 0}\end{matrix}.} $

In an embodiment, the check information update unit B23 is configured tocalculate the check node by using a formula

${\delta_{ij} = {{2{\tanh^{- 1}( {\prod\limits_{j^{\prime} \in {{N{(i)}}\backslash j}}\;{\tanh( {\lambda_{j^{\prime}i}\text{/}2} )}} )}\mspace{14mu}{or}\mspace{14mu}\delta_{ij}} = {{\min( {\lambda_{j^{\prime}i}} )}( {\prod\limits_{j^{\prime} \in {{N{(i)}}\backslash j}}{{sign}( \lambda_{j^{\prime}i} )}} )}}},$and update the check information, where δ_(ij) is the check information,and represents a log-likelihood ratio when other variable nodes exceptthe j^(th) variable node provide information; λ_(j′i) is the informationmessage, and represents a log-likelihood ratio when other check nodesexcept the i^(th) check node provide information; N(i) is a partialelement information set constrained by the check node; N(i)\j representsa subset of N(i) that does not include the j^(th) variable node; and Πis a continuous multiplication operation.

The information message update unit B24 is configured to calculate thevariable node by using a formula

${\lambda_{ji} = {{{llr}( x_{j} )} + {\sum\limits_{i^{\prime} \in {{M{(j)}}\backslash i}}\delta_{i^{\prime}j}}}},$and update the information message.

The log-likelihood ratio update unit B25 is configured to calculate thelog-likelihood ratio when all the check nodes related to the informationbits provide information by using a formula

${\lambda_{j} = {{{llr}( x_{j} )} + {\sum\limits_{i^{\prime} \in {M{(j)}}}\delta_{i^{\prime}j}}}},$where

x_(j) is a transmit codeword in a transmit signal of a transmitter;y_(j) is a receive codeword in the input signal received by a receiver;M(j) is a check set in which the variable node participates; M(j)\irepresents a subset of the M(j) that does not include the i^(th) checknode; δ_(i′j) is the check information, and represents a log-likelihoodratio when other variable nodes except the j^(th) variable node provideinformation; llr(x_(j)) is a representation form of a log-likelihoodratio when the receiver initially receives channel information; λ_(ji)is the information message, and represents a log-likelihood ratio whenother check nodes except the i^(th) check node provide information; andλ_(j) represents the log-likelihood ratio when all the check nodesrelated to the information bits provide information.

The overlapped multiplexing-based demodulation device provided in thisembodiment is corresponding to the overlapped multiplexing-baseddemodulation method provided in Embodiment 2. Therefore, a principle ofthe device is not described in detail herein.

The embodiments of this application provide the overlappedmultiplexing-based modulation and demodulation method and device. In themodulation method, a precoding structure is used, and a transmit endfirst performs parity check product code-based coding on an inputinformation sequence, then performs overlapped multiplexing-basedmodulation and coding, and transmits a coded signal by using an antenna.In the demodulation method, a signal is transmitted by using a channel,and after receiving the signal by using an antenna, a receive end firstperforms digital signal processing, including processes such assynchronization and equalization, then performs overlappedmultiplexing-based demodulation and decoding, and finally performsfactor graph-based belief propagation decoding on a decoding result, tofinally obtain a decoded sequence. In this application, a productcode-based decoding method is used, a parity check code is used as asubcode, and a belief propagation idea of a factor graph is applied to adecoder end. Therefore, a parity check product code in a simplestructure is used. In addition, in the method, the factor graph is usedin a decoding process, thereby reducing operation complexity.

It should be noted that the overlapped multiplexing-based modulation anddemodulation method and device provided in the embodiments of thisapplication may be applied to wireless communications systems such asmobile communications, satellite communications, microwave line-of-sightcommunications, scatter communications, atmospheric opticalcommunications, infrared communications, and underwater acousticcommunications systems; and may be applied to both large-capacitywireless transmission and small-capacity lightweight radio systems.

A person skilled in the art may understand that all or some of the stepsof the methods in the foregoing implementations may be implemented by aprogram controlling related hardware. The program may be stored in acomputer-readable storage medium. The storage medium may include aread-only memory, a random access memory, a magnetic disk, an opticaldisk, or the like.

The foregoing content is a further detailed description of thisapplication with reference to specific embodiments, and it should not beconsidered that specific implementation of this application is limitedonly to the description. A person of ordinary skill in the technicalfield to which this application belongs may further make simplederivations or replacements without departing from the inventive conceptof this application.

What is claimed is:
 1. An overlapped multiplexing-based modulationmethod, comprising: obtaining input information; performing parity checkproduct code-based coding on the input information, to generate a factorgraph; performing overlapped multiplexing-based modulation and coding;and transmitting a coded signal; wherein the performing parity checkproduct code-based coding on the input information comprises: fillingthe input information into information bits in a coding structure;performing row coding on the information in the information bits;performing column coding on the information in the information bits; andgenerating the factor graph for a coding result according to a codingrule; wherein the performing parity check product code-based coding onthe input information further comprises: writing an input informationsequent into corresponding information bits according to a k_(c)×k_(r)two-dimensional structure, wherein a length of the input information isN=k_(c)×k_(r), wherein k_(r) represents a quantity of rows, and k_(c)represents a quantity of columns; performing row coding by assuming thatinformation in the (k_(r)+1)^(th) bit of each row is a modulo-2 additionresult of the first k_(c) ^(th) columns of the current row; performingcolumn coding by assuming that information in the (k_(c)+1)^(th) bit ofeach column is a modulo-2 addition result of the first k_(r) ^(th) rowsof the current column; and generating the factor graph for the codingresult according to the coding rule.
 2. The method according to claim 1,wherein the coding structure is a diagonal coding structure, atwo-dimensional coding structure, a three-dimensional coding structure,or a four-dimensional coding structure.
 3. An overlappedmultiplexing-based demodulation method, comprising: obtaining an inputsignal; performing overlapped multiplexing-based demodulation anddecoding on the input signal; performing factor graph-based beliefpropagation decoding; and outputting a decoding result; wherein theperforming factor graph-based belief propagation decoding comprises:calculating an initial log-likelihood ratio; setting a maximum quantityof iterations; calculating a check node and updating check information;calculating a variable node and updating an information message;calculating a log-likelihood ratio when all check nodes related toinformation bits provide information; performing decision; andoutputting the decoding result after a specific preset condition issatisfied.
 4. The method according to claim 3, comprising: calculatingthe check node by using a formula${\delta_{ij} = {{2{\tanh^{- 1}( {\prod\limits_{j^{\prime} \in {{N{(i)}}\backslash j}}\;{\tanh( {\lambda_{j^{\prime}i}\text{/}2} )}} )}\mspace{14mu}{or}\mspace{14mu}\delta_{ij}} = {{\min( {\lambda_{j^{\prime}i}} )}( {\prod\limits_{j^{\prime} \in {{N{(i)}}\backslash j}}{{sign}( \lambda_{j^{\prime}i} )}} )}}},$and updating the check information, wherein δ_(ij), is the checkinformation, and represents a log-likelihood ratio when other variablenodes except the j^(th) variable node provide information; λ_(j′i) theinformation message, and represents a log-likelihood ratio when othercheck nodes except the i^(th) check node provide information; N(i) is apartial element information set constrained by the check node; N(i)\jrepresents a subset of N(i) that does not comprise the j^(th) variablenode; and Π is a continuous multiplication operation; and/or the presetcondition is that the maximum quantity of iterations is reached.
 5. Themethod according to claim 3, comprising: calculating the variable nodeby using a formula${\lambda_{ji} = {{{llr}( x_{j} )} + {\sum\limits_{i^{\prime} \in {{M{(j)}}\backslash i}}\delta_{i^{\prime}j}}}},$and updating the information message; and calculating the log-likelihoodratio when all the check nodes related to the information bits provideinformation by using a formula${\lambda_{j} = {{{llr}( x_{j} )} + {\sum\limits_{i^{\prime} \in {M{(j)}}}\delta_{i^{\prime}j}}}},$wherein x_(j) is a transmit codeword in a transmit signal of atransmitter; y_(j) is a receive codeword in the input signal received bya receiver; M(j) is a check set in which the variable node participates;M(j)\i represents a subset of the M(j) that does not comprise the i^(th)check node; δ_(i′j) is the check information, and represents alog-likelihood ratio when other variable nodes except the j^(th)variable node provide information; llr(x_(j)) is a representation formof a log-likelihood ratio when the receiver initially receives channelinformation; λ_(ji) the information message, and represents alog-likelihood ratio when other check nodes except the i^(th) check nodeprovide information; and λ_(j) represents the log-likelihood ratio whenall the check nodes related to the information bits provide information.6. An overlapped multiplexing-based modulation device, which comprises ahardware processor and a memory, and the hardware processor is configureto executed programming modules stored in the memory, and theprogramming modules comprising: an input information obtaining module,configured to obtain input information; a parity check productcode-based coding module, configured to perform parity check productcode-based coding on the input information; an overlappedmultiplexing-based modulation and coding module, configured to performoverlapped multiplexing-based modulation and coding; and a signaltransmission module, configured to transmit a coded signal; the paritycheck product code-based coding module is further configured to: writean input information sequent into corresponding information bitsaccording to a k_(c)×k_(r) two-dimensional structure, wherein a lengthof the input information is N=k_(c)×k_(r), wherein k_(r) represents aquantity of rows, and k_(c) represents a quantity of columns; performrow coding by assuming that information in the (k_(r)+1)^(th) bit ofeach row is a modulo-2 addition result of the first k_(c) ^(th) columnsof the current row; perform column coding by assuming that informationin the (k_(c)+1)^(th) bit of each column is a modulo-2 addition resultof the first k_(r) ^(th) rows of the current column; and generate thefactor graph for the coding result according to the coding rule.
 7. Theoverlapped multiplexing-based demodulation device according to claim 6,the programming modules further comprising: a second input signalobtaining module, configured to obtain an input signal; an overlappedmultiplexing-based demodulation and decoding module, configured toperform overlapped multiplexing-based demodulation and decoding on theinput signal; a factor graph-based belief propagation decoding module,configured to perform factor graph-based belief propagation decoding;and a decoding result output module, configured to output a decodingresult; wherein the factor graph-based belief propagation decodingmodule is further configured to: calculate an initial log-likelihoodratio; set a maximum quantity of iterations; calculate a check node andupdating check information; calculate a variable node and updating aninformation message; calculate a log-likelihood ratio when all checknodes related to information bits provide information; perform decision;and output the decoding result after a specific preset condition issatisfied.